Invasive Species Traits

Introduction to Invasive Species and Their Traits

In this lecture, we will explore the role of species traits in predicting whether certain species can become invasive. We will begin by identifying specific invaders and examining whether they share common traits that can serve as indicators of their invasiveness.

Examples of Invasive Species

Aquatic Plants

  1. Hydrilla

    • Origin: Southern Asia
    • Introduced in: Europe, Australia, North America, Africa
    • Habitat: Freshwater systems (lakes, rivers, streams)
    • Introduction Vector: Aquarium trade

  2. Water Hyacinth

    • Origin: Amazon Basin
    • Introduced in: Over 50 countries in tropics and subtropics (Africa and North America)
    • Habitat: Freshwater
    • Introduction Vector: Aquarium trade, used as ornamental plant for ponds

  3. Lophocladia lallemandii

    • Type: Red alga
    • Origin: Red Sea
    • Introduced in: Mediterranean Sea (via Suez Canal)
    • Habitat: Marine; grows on rocky bottoms and over seaweeds

  4. Undaria pinnatifida (Wakame)

    • Origin: Asia
    • Introduced in: European coat, Atlantic and Mediterranean, Argentina, New Zealand, West Coast of North America
    • Habitat: Marine
    • Introduction Vector: Aquaculture, food popularity, other vectors including tsunami debris

Invertebrate Species

  1. Mneiopsis leidyi

    • Type: Ctenophore (gelatinous plankton)
    • Origin: Atlantic coast of North and South America
    • Introduced in: Europe, Black Sea, Azov Sea, Caspian Sea
    • Introduction Vector: Ballast water

  2. Zebra Mussel

    • Origin: Caspian and Black Seas
    • Introduced in: US, Atlantic coast of Europe
    • Habitat: Freshwater
    • Introduction Vector: Ballast waters

  3. Red Swam Crayfish

    • Origin: Northeastern Mexico, South-Central US
    • Introduced in: Central and South America, eastern Asia, parts of eastern and southern Africa, Southern Central and Western Europe, east and west coast of the US
    • Habitat: Freshwater
    • Introduction Vector: Aquaculture

Vertebrate Species

  1. Bullfrog

    • Origin: Eastern US
    • Introduced in: Western North America, Europe, South America, Asia
    • Habitat: Freshwater (ponds, marshes, streams, canals)
    • Introduction Vector: Purposeful introduction for food and hunting

  2. Lionfish

    • Species: Pterois volitans, Pterois miles
    • Origin: Indo-Pacific
    • Introduced in: Caribbean, Southeast US
    • Habitat: Marine
    • Introduction Vector: Aquarium trade

  3. Nile Perch

    • Origin: African great rivers
    • Introduced in: Lake Victoria, other African river basins
    • Habitat: Freshwater
    • Introduction Vector: Enhancement of fishing

  4. Nutria (Myocastor coypu)

    • Origin: South America
    • Introduced in: US
    • Purpose: Fur farming industry
    • Habitat: Freshwater

Common Traits of Invasive Species

Having observed a range of invasive species, we must consider whether there are shared traits that contribute to their success as invaders. If certain traits promote invasiveness, identifying these could help predict and possibly prevent invasions. Key traits include:

  • Reproductive Traits: Invasive species often have high rates of reproduction both sexually and asexually, producing large numbers of offspring with short generation times.
  • Dispersal Mechanisms: Effective dispersal is crucial for the success of invasives.
  • Generalist Adaptability: Many invasive species can thrive across a wide range of environmental conditions, diets, or other adaptations.

Trait Analysis in Invasive Species

Review by Kolar and Lodge (2002)

The review conducted by Kolar and Lodge focused on plants and birds, identifying and differentiating between traits relevant during the establishment phase versus the spread phase of invasives.
Examples of traits analyzed:

  • Biological Traits: Number of eggs produced, dispersal mechanisms, longevity, height/body length, length of juvenile period
  • Behavioral Traits: Diet breadth/type
  • Biogeographical/Ecological Traits: Origin, taxon, range, habitat.

Research by Rejmanek and Richardson

A notable study analyzed 24 species of pine trees introduced worldwide, assessing life-history traits that might explain invasiveness. Ten traits were evaluated, including:

  • Mean height
  • Maximum height
  • Minimum juvenile period
  • Mean longevity
  • Mean seed mass
  • Seed-wing loading index
  • Average percent germination
  • Mean interval between large seed crops
  • Degree of serotiny
  • Fire tolerance index

They found only three traits significantly correlated with the likelihood of invasion: juvenile period, seed mass, interval between large seed crops.

Study by Godoy et al (2011)

This review examined differences in traits between native and invasive species, emphasizing the effects of nutrient and light levels. Key findings include:

  • Invasive species generally exhibited higher above and below-ground biomass at mid/high nutrient levels.
  • In low nutrient scenarios, invasives did not outperform natives.
  • Notably, invasives did not consistently show higher survival compared to natives, except in low light/high nutrient conditions.

Meta-Analysis by Van Kleunen et al

Van Kleunen and colleagues conducted an extensive meta-analysis comparing a range of traits between invasive and non-invasive plants. The study utilized effect size metrics, specifically Hedges d, to quantify results across studies. Key aspects examined included:

  • Fitness Traits: Seed and flower counts, fruit germination traits, survival metrics.
  • Size and Growth Traits: Biomass and height measures, growth rates.
  • Physiological Traits: Rates of photosynthesis, transpiration, nitrogen utilization efficiency.

Findings indicated that invasive species consistently had higher values than non-invasive species across all analyzed traits.

Aquatic Species Studies

  1. Grabowski et al Review: Compared life history traits of introduced and native gammarids in Central European waters. Exotic gammarids exhibited traits such as larger brood sizes, high fecundity, early maturation.

    • Multivariate analysis distinguished natives from exotics effectively based on reproductive traits.

  2. Stranzer et al Review: Analyzed invasive stream macroinvertebrates in Europe, demonstrating that invasive genera tended to reproduce more frequently, and had traits favoring survival during dispersal (e.g., size and lifespan).

  3. Nyberg and Wallentinus Analysis: Compared invasive macroalgae traits, focusing on survival out of water, salinity and temperature tolerance, and methods of reproduction.

    • Findings suggested significant differences in invasiveness between groups based on the aforementioned traits. Green algae demonstrated high survival out of water and salinity tolerance, while brown algae excelled in fragmentation and defense mechanisms.

Conclusion

The analysis of invasive species shows specific traits that enhance their success, though these traits vary significantly across different taxa and invasion stages. It is crucial to analyze traits with detail to fully understand the factors contributing to invasion. Furthermore, there are clearer contrasts in traits between native and introduced species than between invasive and non-invasive populations. Understanding these differences may help guide future invasive species management strategies.